Protective system for highway crossings



United States Patent 3,176,126 PROTECTIVE SYSTEM FOR HIGHWAY CROSSINGS Edwin G. Vineall, Rochester, N.Y., assignor to General Signal Corporation Filed Jan. 11, 1961, Ser. No. 82,038 Claims. (Cl. 246-125) This invention relates to highway crossing protective systems for railroads, and it more particularly relates to highway crossing systems which provide a warning and/ or a stop control for an approaching train whenever an obstruction, such as a stalled vehicle or the like, is on the intersection of a highway and the railroad tracks.

The underlying concept of present day highway crossing protection system is to prevent accidents by prealerting the occupants of vehicles using a highway crossing to the presence of a train approaching the highway crossing. The systems in general use provide some form of warning device, such as signals adjacent the intersection of the highway and the railroad tracks which are actuated by detection means, usually in the form of a track relay, responsive to the presence of an approaching train at some predetermined location and over the distance between that location and the crossing.

Such signals are controlled to provide a twenty second warning time upon the approach of a train. For example, if the top speed of trains travelling over a given stretch of track is sixty miles per hour, then the approach distance for operating the highway warning device would be approximately 1800 feet. Since a train travelling at sixty miles per hour requires a stopping distance of approximately 6000 feet, it is rather obvious that should a vehicle become stalled on the tracks at a highway crossing, the engineman on an approaching train could not see and determine such stalled condition in time to 'bring the train to a stop in time to avoid a collision. This assumes normal sighting distances in two or three thousand feet on straight track, but it is obvious that such sighting distance might be limited by curves and obstructions, along the railroad track.

However, whenever automatic train control is in effect, means can be provided to detect the presence of a stalled vehicle on the tracks at the highway crossing and cause an automatic control of the train at considerably greater distances than can be considered a reasonable sighting distance by the usual engineman, and cause an automatic stopping of the train in advance of the highway crossing and thus an avoidance of a collision. This of course could be effected regardless of the curvature and sighting distances involved along the railroad track and regardless of various other factors such as Weather conditions, time of day, and train speed.

Certain highway crossing protection system employ what has become to be known as short arm gates which are automatically lowered into position upon the approach of a train. Each such gate obstructs only one lane of the highway. This arrangement allows a vehicle having once passed a gate to freely continue its passage beyond the crossing even though that gate has become lowered. This type of protection is particularly effective in preventing vehicles from racing the train, so to speak, since it prevents entrance upon the trackway during the last seconds of safety. With this kind of protection many collisions at highway crossings have been prevented.

There have been other proposals in which a sweeptype gate is arranged to normally block the trackway but is moved into position to prevent the highway traflic from crossing the track upon the approach of a train. Such gate is arranged to sweep over that portion of the highway immediately adjacent the track so as to assure that there is no stalled vehicle on the track. It is then pro posed that such sweeptype gate control a signal to cause the stopping of a train should it encounter an obstruction on that portion of the highway immediately adjacent the tracks.

This sweeptype gate protection for highway crossings is not adaptable to the usual highway involving vehicle trafiic travelling at the speeds now normally encountered. It is rather obvious that such a sweeptype gate could be moving to an obstructing position on the highway at a time relative to the approach of a vehicle at speed on the highway so that the vehicle could not stop in time to avoid a collision with the gate. Such an organization, however, not only would prevent vehicles from movement over the tracks during the last seconds of safety but would also prevent the crossing of vehicles during the safe periods immediately following the initiation of the signal indicating the approach of a train. This type of organization would therefore require that the approach of the train initiate the closing of the gate to highway trafiic when the train was at a point where it could still be stopped and then cause a sweeping of the crossing, so to speak, to determine whether or not the train should be stopped. Although this might be feasible if all trains travelled at the same speed, it would be impractical since the slow trains would require such a long time to pass the crossing over the long approach distances thus required, the vehicle traflic on the highway would be unduly impeded.

In addition, if such sweeptype gate should detect a temporary obstruction, the system would act in the usual way and efiect an emergency stopping of the train although there might be no continuing cause for stopping the train. In addition, a sweeptype gate inherently is a fully blocking type of device so that in its operation it is not possible for a vehicle temporarily stalled to continue on its way as soon as it again becomes mobile.

Generally speaking, and without making any attempt to describe the exact form of the present invention, it is proposed to provide a highway crossing with means for detecting a stalled vehicle on the portion of highway immediately adjacent the track, without in any way obstructing either the highway or the track. The detection of a stalled vehicle on the track would provide an adequate warning to an approaching train regardless of Whether it is automatically operated or handled by an engineman, to stop short of the obstruction on the track. However, the means for detecting the presence of a stalled vehicle is also effective to cancel its effect on an approaching train in the event the vehicle becomes mobile.

The system contemplated by the present invention will allow the normal passage of trailic up to the usual twenty second warning time and then provide short arm gate protection in the usual way; but in the event of a stalled vehicle, the warning signals will be given upon the approach of a train at a much earlier time although the short arm gates are not moved into position until slightly after the usual twenty second protecting time. In any event, the stalled vehicle is always free to become mobile and proceed in the direction normally intended to be travelled.

A detector for stalled vehicles on the crossing which does not require objectionable barriers such as have been heretofore employed is provided by the present invention in the form of detector units disposed at the crossing detecting the presence of vehicles on the crossing by waves of a supersonic or ultrahigh frequency reflected from the vehicles, in combination with apparatus provided for determining whether or not the vehicles are in motion. One such means for detecting a stalled vehicle, for example, is to time the period during which a reflected signal is received from the vehicle at the crossing. If the signal is received continuously for a period of time greater than the time required for a vehicle to proceed across the tracks, an indication is registered that the vehicle is stalled on the tracks, and that if a train is approaching, it should be stopped by application of the brakes at a point well in approach of the normal approach control point for starting the conventional highway warning devices at the crossing.

Although the present invention contemplates that a stalled vehicle on the highway crossing the tracks will effeet a warning to an approaching train in suflicient time to eifect the stopping of such train, it can be appreciated that the stalling of the vehicle and the approaching of the train can take place during such a critical period or combination of circumstances that this cannot be effected in any event, in which case the apparatus of the present invention eflects a stop operation of the train without modifying control to cause the train to come to an absolute stop. This assures automatic stoppage of such train until :the situation with regard to a collision or near collision has been fully investigated, and authorized personnel have approved further operation of the train.

In view of the above, it can be stated that one of the objects of the present invention is to provide means for detecting the presence of a stalled vehicle or other obstruction on a highway crossing and giving a warning signal to an approaching train in time adequate for the train to stop short of such obstruction.

Another object of the present invention is to detect the presence of stalled vehicles on a highway crossing, without theuse of barriers, by employing tratfic detector units at the crossing operating on a reflected wave principle.

Another object of the present invention is to render the detection of a stalled vehicle on a crossing effective prior to the time for the normal actuation of highway crossing signals upon the approach of a train.

Another object of the present invention is to control wayside signals on the railroad and/ or train stop apparatus selectively in accordance with the detection of a stalled vehicle on a highway crossing.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawing and in part pointed out as the description of the invention progresses.

In describing the invention in detail, reference is made to the accompanying drawings in which similar reference characters are used for the identification of corresponding apparatus in the different figures, and in which:

FIG. 1 illustrates one embodiment of the system provided according to the present invention for the protection of vehicles at a highway crossing; and,

FIG. 2 illustrates apparatus for registering the presence of traffic at a highway crossing based upon the reflection of energy from the vehicles.

For the purpose of simplifying the illustration and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional elements have been shown in block form, the drawings having been made more with the purpose of making it easy .to understand the principles and mode of operation than with the idea of illustrating the specific construction and arrangements of parts that would be employed in practice. The symbols (-1-) and are employed to indicate the positive and negative terminals respectively of suitable batteries, or other sources of direct current; and the circuits with which these symbols are used always have current flowing in the same direction.

Although one particular embodiment of the present invention is disclosed as being applied to obstructions on intersections on a highway of a railroad track, it is to be understood that the present invention may be applied as a warning system for obstructions in connection with the movement of objects along practically any form of intersecting fixed paths.

With reference to FIG. 1, one embodiment of the present invention is shown as being applied to a stretch of railway track 10 divided into adjoining track sections AT, 1T, 2T, ST and 4T, the track section 3T extending through a crossing of a highway 11. Each of the track sections T has a conventional track circuit associated therewith including a normally energized track relay TR.

Signals S are provided for governing the entrance of trains into the several track sections for westbound trafiic (traflic from right to left). These signals provide the usual proceed, caution, and stop aspects, and in addition each of the signals S is provided with a special aspect, such as a lunar white lamp LW, which is illuminated when an aspect is to be displayed that a train is being stopped because of an obstruction on the highway crossing. Normally energized home relays H of the polar-neutral type are provided for the control of the several signals for selecting the signal aspects to be displayed by the associated signals in accordance with the condition of occupancy of the various track sections.

Short arm crossing gates 12 and flashing light signals 13 are provided at the highway crossing at both sides of the track in accordance with usual practice for stopping highway traflic for the passage of trains. A normally energized relay GR is provided for the control of the gates, and a normally energized relay XR is provided for the control of the crossing signals.

Traflic detecting apparatus, including transmitter-receiver transducers T-Rl, T-RZ and T-R3 is provided at the highway crossing, including detector apparatus 14 and a normally deenergized crossing occupancy detector relay XOR for the purpose of registering the presence of traf fic on the crossing.

With reference to FIG. 2, the Transmitter-Receiver Transducers T-R are disposed above the highway at the crossing for the transmission of supersonic pulses downwardly to be reflected back .to the receiving apparatus, both by the highway and by vehicles passing under the detectors. Control apparatus is provided for the energization of relay XOR to register the presence of traffic only when traffic is detected as being beneath the Transmitter-Receiver Transducers. Such detection is determined by the shorter time of reflection of supersonic pulses from the top of vehicles than the time required for reflection from the pavement. The system for the control of the relay XOR which is illustrated by block diagram in FIG. 2 illustrates the general organization of the supersonic detection system, and reference can be made to the prior US. patent application of H. C. Kendall et a1., Ser. No. 808,736, filed April 24, 1959, which has resulted in Patent No. 3,042,303, granted July 3, 1962, for disclosure of details of the supersonic detection system.

The system according to FIG. 2 includes an Ultrasonic Pulse Generator 15 which has an output feeding to a Hybrid Transformer Network 16 for each of the Transmitter-Receiver Transducers T-R. Each of the Hybrid Transformer Networks 16 has an output connected to its associated Transmitter-Receiver Transducer 17, and each of the Hybrid Transformer Networks 16 has an output which is applied to Reflected Pulse Recep tion apparatus 18, which in turn has an output applied to Gated Detection apparatus 19. The Gated Detection apparatus 19 is governed by Gate Timing apparatus 20, which in turn is controlled by the Ultrasonic Pulse Generator 15.

As a means for enforcing the stopping of trains, which may or may not be under manual operation, inductors I are disposed at the signal locations as a part of intermittent train control apparatus that can be provided for the control of trains. The use of such inductors for in termittent inductive train control purposes is well known to those skilled in the art and is disclosed, for example, in detail in the US. patent of C. S. Bushnell Patent No. 1,619,698, granted March 1, 1927.

Normally inactive timers lTE and 2TB and associated thermal units TH are provided as a part of apparatus for detecting as to when a vehicle is stalled on the highway. A time repeater relay TEP is provided for initiating the putting to stop of signals S and the control of inductors I in accordance with the registration of the presence of a stalled vehicle on the highway crossing.

Under normal conditions, with the trackway unoccupied by a train, the green lamps G of the signals S are energized in accordance with the energization of the relays H for the associated signals with positive polarity. Relay 2H is normally energized by a circuit extending from (B+), including front contacts 21, 22, 23, 24 and 25 of relays 3H, 4TR, 3TR, TEP and 2TR respectively, and winding of relay 2H, to (CN). In accordance with the energization of relay 2H, the relay 1H is also normally energized by a circuit including front contact 26 of relay 2H and front contact 27 of relay 1TR. The green lamp G of signal 18 is energized by a circuit including front contact 28 of relay 1H and polar contact 29 of relay 1H in its left-hand position, and similarly the lamp G of signal 28 is normally energized by a circuit including front contact 30 of relay 2H and polar contact 31 of relay 2H in its left-hand position.

The gate control relay GR is normally energized by a circuit including front contact 32 of relay 2TR and front contact 33 of relay 3TR, and the energization of this relay maintains the gates 12 in their normal position. Relay XR is also normally energized for maintaining the signal 13 inactive at the crossing. The circuit for energization of relay XR includes front contact 32 of relay 2TR, front contact 34 of relay TEP and front contact 35 of relay 3TR. Relay TEP is normally maintained energized by a circuit including front contact 36 of relay ATR and front contact 37 of relay lTR. Another normally energized circuit for the relay TEP includes front contact 38 of relay 1TR and back contact 39 of relay 2TB.

To consider the mode of operation of the system upon passage of a train, it will first be assumed that there is no vehicle on the highway crossing, and that an approaching train enters the approach track section AT. The dropping away of relay ATR opens contact 36 in the circuit for relay TEP, but relay TEP does not become dropped away because it is maintained energized through front contact 38 of relay 1TR.

When the train enters the track section 1T, the relay TEP is still maintained energized, even though front contact 38 of relay 1TR is opened, because of energy being applied to that relay through back contact 40 of the timer 1TE. The signal 18 is put to stop by the dropping away of track relay 1TR upon the opening of front contact 27, and in accordance therewith the lamp G of that signal is extinguished and the red lamp R becomes illuminated in accordance with the shifting of contact 28 of relay 1H. It will be noted that there is no illumination of the lunar white lamp LW of either signal 15 or signal 28 because the relay TEP is maintained picked up to hold the circuit open for the energization of these lamps at back contact 41 of relay TEP.

When the train progresses further so as to occupy the track section 2T, the dropping away of relay 2TR causes the dropping away of relay 2H upon the opening of front contact 25, which in turn is effective upon the shifting of its contact 30 to extinguish the green lamp G of signal 28 and energize the red lamp R of that signal.

The dropping away of the track relay 2TR also initiates the flashing of the signal lamps 13 by opening the circuit for relay XR at front contact 32, and the opening of this contact also provides for the deenergization of the gate control relay GR, which operates the gates 12 to a horizontal position. The relay GR is made slow to release so that the crossing signals are energized for a short period of time by the closure of back contact 42 prior to the operation of the gates in accordance with the closure of back contact 43 of relay GR.

The gates 12 and the crossing signals 13 are maintained in their operated positions while the train is operated over the highway crossing, and even though the presence of the train on the crossing may actuate the relay XOR because of being detected by the vehicle detector, the closure of front contact 44 of the vehicle registering relay XOR cannot cause operation of the timers 1TB and 2TB because the front contact 45 of relay 3TR is open at that time. In other words, this circuit organization provides that the means provided for registering a stalled vehicle on the crossing distinguishes between whether there is a vehicle stalled on the crossing or whether the crossing is occupied by a train in accordance with whether or not the track section 3T is shunted so as to cause the release of the track relay 3TR. It will be readily apparent that, after passage of the train, conditions are restored to normal in accordance with the energization of the track relays TR for the respective track sections as such track sections become unoccupied in the rear of the train. The gates 12 are raised and the flashing crossing signal 13 is rendered inactive in accordance with the track sections 2T and 3T becoming unoccupied in the rear of the train.

A condition of operation will now be considered when a vehicle becomes stalled on the railway tracks at the crossing prior to the approach of a train. The presence of the vehicle causes the picking up of the vehicle occupancy relay XOR, and the picking up of this relay, with the track section 3TR unoccupied by a train, renders the thermal relay 1TH operable to time an interval as a means of detecting as to whether or not the vehicle is stalled on the track. The winding of the thermal relay 1TH is energized through front contacts 44 and 45 of relay XOR and 3TR respectively, and through back contact 46 of the timing relay 1TE. After the thermal relay 1TH has completed its operation, a circuit is closed through its contact 47 to energize the timer relay 1TB, and the relay 1TE is maintained energized by a stick circuit wherein front contact 46 of relay 1TE shunts the contact 47 of the thermal relay 1TH out of the circuit by which relay 1TB has become picked up. Relay 1TB is effective upon its energization to initiate the operation of the thermal relay 2TH upon the closure of front contact 48, and the closure of contact 49 of the thermal relay 2TH causes the picking up of relay ZTE through front contact 48 of relay 1TE. This relay when picked up is maintained energized by a stick circuit including front contact 48 of relay 1TE, winding of thermal relay 2TH and front contact 50 of relay 2TB.

Because of the timing relays 1TE and 2TB being both operated to their picked up positions, it is determined that the occupancy of the highway 11 at the crossing continuously for this time interval is indicative of a vehicle having stopped on the crossing.

When a train approaches and enters the approach track section AT, the relay TEP becomes dropped away upon the opening of front contact 36 of relay ATR because of contacts 40 and 39 of timing relays 1TE and 2TE having been opened in the control circuit for the relay TEP. The dropping away of relay TEP immediately energizes the lunar white lamps LW of both signals 18 and 28 upon the closure of back contact 41, and it also causes the dropping away of relays 2H and 1H by the opening of front contact 24 in the control circuit for relay 2H. The dropping away of relay 2H causes the extinguishing of the green lamp G of signal 28 and the energization of the red lamp R upon the shifting of contact 30, and similarly the green lamp G of signal 18 becomes extinguished and the red lamp R of that signal becomes illuminated by the shifting of contact 28 of relay 1H. Thus a stop signal is displayed for the train, and the energization of the lunar white lamps LW indicate to the engineman that the train is being stopped because of the presence of a vehicle stopped on the crossing. With the display of a stop signal by the signal 18 at a point well in approach of the crossing, the train can be brought to stop to avoid a collision as has been heretofore pointed out in considering the general mode of operation of the system. It will be noted that the crossing signals 13 are also rendered active at this time by the opening of front contact 34 of relay TEP in the circuit for relay XR so that back contact 42 of relay XR becomes closed to initiate operation of the crossing signals. This indicates to the operator of the vehicle on the crossing that a train is approaching, but the gates 12 remain raised to permit progress of the vehicle off of the crossing if such operation is possible.

It will also be noted that the dropping away of relay 1H opens the circuit for the winding of the Wayside inductor A1 at front contact 51 so that in case the engineman does not see the stop signal, or in case the approaching train is under automatic operation, the train will be brought to a stop in time to avoid a collision.

When the train enters the track section 2T, the dropping away of relay ZTR causes the gates 12 to be lowered in accordance with the opening of the circuit for the gate control relay GR at front contact 32.

Any time that the vehicle occupying the crossing moves off of the crossing, the detector relay XOR becomes dropped away, and in accordance with the dropping away of that relay, the stick circuit for relay lTE is opened at front contact 46, and the dropping away of relay ITE opens the stick circuit for relay 2TB at front contact 48 so as to cause the dropping away of that relay. With relays 1TB and 2TB both in their dropped away positions, a circuit that has been described for the relay TEP is closed so as to cause the picking up of this relay. The picking up of relay TEP opens the circuit for the lunar white lamps LW of signals 15 and 28 at back contact 41 to cause the extinguishing of these lamps. The closure of front contact 24 of relay TEP in the circuit for relay 2H conditions the circuit for relay 2H so that relay 2H can be energized after passage of the train in a manner which has been heretofore described. Similarly the closure of front contact 34 of relay TEP conditions a circuit so that the crossing signal control relay XR can become picked up after passage of the train over the crossing.

In case the vehicle occupying the crossing does not move off of the crossing before the approaching train occupies the track section 3T, the dropping away of relay 3TR is effective to cause the resetting of the timers 1T E and 2TB and the relay TEP because of the opening of front contact 45 in the stick circuit for the relay lTE. It will thus be readily apparent that the relays lTE, 2TB and TEP can be reset either by the crossing becoming unoccupied by a vehicle that may have been stalled there, or by the presence of the train in the crossing track section 3T so as to cause the dropping away of the track relay 3TR.

The mode of operation as heretofore described has been under an assumed condition where a vehicle has been detected as being on the crossing for a period of time suificient' for the timing relays 1TB and 2TE to both become energized before a train occupies the approach track section AT. It will be readily apparent that there may be other conditions where a vehicle may become stalled on the tracks at a time when a train is more closely in approach of the highway, and under such conditions it has been considered desirable to stop the train even though only a relatively short time interval as timed by the relay 1TB has been indicative of the vehicle being stalled on the tracks. In other words, if the tracks at the crossing are occupied by a highway vehicle for a time sufficient to operate both of the timing relays lTE and ZTE sequentially, the time interval is such that there is no question but what the vehicle is stalled on the tracks. On the other hand, if only the time required for operation of the relay 1TE has elapsed, this may be indicative of a stalled vehicle, but yet could also be indicative of the presence of a long truck, for example, proceeding very slowly across the crossing.

It has been considered, however, that if a train is as close to the crossing as to have occupied the track section IT at a time when only the timer 1TB has had time to be operated, that the signal 28 should be put to stop, and the inductor 11 unshunted by the opening of contact 52 so that the approaching train will be brought to a stop in time to avoid a collision, or will be reduced in speed sufficiently to provide time for the occupants of the stalled vehicle to vacate the vehicle. Thus it is considered desirable to have the two separate timing periods wherein both periods are used to positively detecting a stalled vehicle when a train is remotely in approach of the crossing, and to use only a single timer when a train is more immediately in approach of the crossing to detect a possibly stalled vehicle so as to provide added time for the vehicle to clear the crossing.

Under the condition described where only one timing relay lTE is operated, the timing and detector apparatus is restored to normal upon passage of the train in a manner similar to that which has been described, except that the relay TEP becomes picked up at a time when the track section 1T becomes unoccupied in the rear of the train so as to cause the picking up of relay 1TR, which in turn closes front contact 38 to provide for the picking up of relay TEP through back contact 39 of relay 2TB.

Having thus described a warning system for a highway crossing as one embodiment of the present invention, it is to he understood that various adaptations, alterations and modifications may be applied to the specific form shown and described in accordance with the requirements of practice within the scope of the present invention except as limited by the appending claims.

What I claim is:

1. A protective system for vehicles at a grade crossing between a railroad track and a highway comprising, a vehicle detector at the crossing for registering the presence of a highway vehicle on the crossing, a timer initiated by the registration of the presence of a vehicle on the crossing by said vehicle detector which timer is operable to an actuated position a predetermined time after its initiation, and means controlled by said vehicle detector after said timer has been operated toits actuated position for effecting a stop control for a train approaching said crossing on said railroad track.

2. A warning system for protection against collision of vehicles at a grade crossing of a right-of-Way and a highway comprising, normally clear signals operable selectively to provide clear and stop indications for governing trafiic along the right-of-way in approach of the crossing, a vehicle detector at the crossing for registering the presence of a highway vehicle on the crossing in accordance with the detection of a signal reflected from the vehicle, a timer initiated by the registration of the presence of a vehicle on the crossing by said vehicle detector operable to an actuated position a predetermined time after its initiation, and means including said vehicle detector and said timer for operating said signals to provide a stop indication when said crossing has been occupied by a highway vehicle long enough for the operation of said timer to said actuated position.

3. A warning system according to claim 2 wherein the vehicle detector includes at least one supersonic transmitter-receiver disposed to transmit and receive supersonic pulses in the direction of vehicles occupying the crossing.

4. A warning system according to claim 3 wherein the supersonic transmitter-receivers are disposed above the highway at the crossing and directed downwardly in the direction of the highway.

5. A warning system for protection against collision of vehicles at a grade crossing of a railroad and a highway comprising, train control apparatus partly on a train and partly at the wayside along the railroad operable selectively to apply or not apply the brakes of the train when the train reaches a particular point along the railroad in approach of the crossing, a vehicle detector at the crossing for registering the presence of a highway vehicle on the crossing in accordance with the detection of a signal reflected from the vehicle, a timer initiated by the registration of the presence of the vehicle on the crossing by said vehicle detector operable to an actuated position a predetermined time after its initiation, and means responsive to said vehicle detector and said timer for operating said train control apparatus to apply the brakes of the train when the crossing is occupied by a vehicle for a predetermined time interval.

6. A warning system according to claim wherein said train control apparatus includes at least one wayside inductor disposed along the railroad right-of-way a substantial distance in approach of the crossing.

7. A warning system according to claim 5 wherein the vehicle detector includes at least one sonic transmitterreceiver disposed to transmit and receive supersonic pulses in the direction of vehicle occupying the crossing.

8. A warning system for protection against collision of vehicles at a grade crossing of a right-ot-way and a highway comprising, normally clear signals operable selectively to provide clear and stop indications for governing tratfic along the right-of-way in approach of the crossing, vehicle detector means including apparatus for the transmission of supersonic pulses in the direction of the highway at the crossing and for the reception of pulses reflected from a vehicle at the crossing, for distinctively registering when a highway vehicle is on the crossing,

timing means controlled by said detector means and including at least one timer for determining that the highway crossing is continuously occupied by a highway vehicle for a time period indicative of the vehicle being stopped on the crossing, and means controlled by said timing means for operating said signals to provide a stop indication in accordance with the determination by said timing means that a vehicle is stopped on the crossing.

9. A warning system according to claim 8 wherein said timing means includes a plurality of timers for timing a plurality of different time intervals and wherein means is provided for operating a signal to stop when a train is relatively close in approach of the crossing after only one of the timers has had time to complete its operation for timing a first interval.

10. A protective system for vehicles at a grade crossing between a railroad track and a highway comprising, a barrier with warning signals normally located in a nonobstructing position but operable to a position for obstructing highway trafiic from moving onto said crossing for the normal directions of approach to the crossing on said highway but allowing a vehicle to leave the crossing in a corresponding direction, a vehicle detector at the crossing for registering the presence of a highway vehicle on the crossing in accordance with the detection of a signal reflected from the vehicle, means responsive to the approach of a train within a predetermined distance for causing said barrier to be moved from its normal position to an obstructing position, and means controlled by said vehicle detector when it has detected a vehicle as being present on said crossing for more than a predetermined time to effect a stop control for an approaching train.

References Cited by the Examiner UNITED STATES PATENTS 2,319,137 5/43 Kitchen 246129 2,494,435 1/50 Freeman 246-1 14 2,569,111 9/51 Miller 246l26 2,629,865 2/53 Barker.

2,718,588 9/55 Baughman 246161 2,719,218 9/55 Miller 246161 2,734,130 2/56 Dodd et a1. 246161 2,768,286 10/56 Kendall 24630 2,847,080 8/58 Zworykin 340-31 3,042,303 7/62 Kendall et al. 23599.1 3,086,195 Vande Sande 340-38 3,102,252 8/63 Bolton 340-38 LEO QUACKENBUSH, Primary Examiner.

JAMES S. SHANK, Examiner. 

1. A PROTECTIVE SYSTEM FOR VEHICLES AT A GRADE CROSSING BETWEEN A RAILROAD TRACK AND A HIGHWAY COMPRISING A VEHICLE DETECTOR AT THE CROSSING FOR REGISTERING THE PRESENCE OF A HIGHWAY VEHICLE ON THE CROSSING, A TIMER INITIATED BY THE REGISTRATION OF THE PRESENCE OF A VEHICLE ON THE CROSSING BY SAID VEHICLE DETECTOR WHICH TIMER IS OPERABLE TO AN ACTUATED POSITON A PREDETERMINED TIME AFTER ITS INTITATION, AND MEANS CONTROLLED BY SAID VEHICLE DETECTOR AFTER SAID TIMER HAS BEEN OPERATED TO ITS ACTUATED POSITION FOR EFFECTING A STOP CONTROL FOR A TRAIN APPROACHING SAID CROSSING ON SAID RAILROAD TRACK. 